1. Field of the Invention
The present invention relates to radio telecommunications systems, particularly to a method and system for protecting co-existent wireless application services interfering with cellular telecommunications systems.
2. Description of the Related Art
Cellular and wireless services are known for a number of years, and become more and more popular. In wireless telephony, frequency spectrum is allocated for supporting radio communications between a network and Mobile Stations (MSs). In every national jurisdiction, a public organism, such as for example the Federal Communications Commission (FCC) in the United States of America has authority to manage the allocation of the frequency spectrum to various wireless applications, such as for example for television broadcasting, cellular telecommunications, public safety radio services (police, fire-fighters, or paramedics radio communications), military transmission applications, and others. Since most frequency spectrum holders try to maximize their investment by using high spectral density transmissions in their allocated bandwidth, the interference generated into neighboring frequency spectrums become important and non-negligible. Frequency guard bands, which are non-assigned bands of frequency spectrum, is one known partial remedy for copping with existing frequency interference generated by one system into a second system""s allocated frequency spectrum.
For better understanding the concept of Out Of Band radio Emissions (OOBEs), reference is now made to FIG. 1.a, wherein there is shown a schematical representation of a frequency spectrum assigned to a radio frequency operator. The allocated frequency spectrum shown in FIG. 1.a has a nominal bandwidth the operator is allowed to use for its radio application, such as for example for operating a cellular telecommunications network. A maximal nominal power level is also set and allowed for the radio transmissions within the nominal bandwidth. However, due to the imperfect nature of transceivers, OOBEs are most always generated outside the nominal bandwidth, as shown. The generated OOBEs may interfere with other radio applications that are allocated the frequency spectrum neighboring the allocated nominal bandwidth.
Reference now being made to FIG. 1.b, wherein there is shown another schematical representation of an allocated frequency spectrum assigned to a radio frequency operator. In FIG. 1.b, the Guard Bands GB A and GB B are used around the assigned nominal bandwidth for coping with OOBE. In such manner, if there are OOBEs, they are generated within the guard bands, which are not used by any other wireless application.
FIG. 2 illustrates an example of a frequency spectrum assigned in the United States of America, where the FCC has decided to re-allocate frequency spectrum formerly used for Ultra-High Frequency (UHF) television channels 60 through 69, both for new wireless services (cellular network operators) and for public safety radio services (operated by police, paramedics, etc). This frequency spectrum ranges from 746 MHz to 806 MHz. A first license of 5 MHz, and a second license of 10 MHz have been assigned in both downlink and uplink cellular applications, as shown. Adjacent to the cellular applications, but separated by 1 and 2 MHz guard bands, were allocated two 12 MHz frequency spectrums for public safety services, one for the downlink radio transmissions (base station to terminals) and one for public safety uplink radio transmissions (terminals to base station). It was noted in many instances that, for example, cellular downlink transmissions effectuated in the frequency band just before the 762 MHz high-end limit, negatively interfere with the public safety downlink transmissions in the frequency band just above the 764 MHz low-end limit. Furthermore, it was also observed that the uplink cellular transmissions effectuated on radio channels just above the frequency of 777 MHz also create OOBE affecting the public safety downlink radio transmissions on channels just below the 776 MHz limit. These problems may further be accentuated in situations wherein there are no guard bands between the cellular network""s spectrum and the coexistent network""s spectrum, and when the two systems"" sub-bands are used for transmission in the same direction (downlink or uplink).
The interference problems described in relation to FIG. 2 can be better understood with reference to FIG. 3, wherein there is shown a schematical representation of a typical near-far type interference problem involving a cellular network 10 which geographical radio coverage overlaps a coexistent public safety radio network 12 radio coverage. As known in the art, the cellular telecommunications network 10 comprises a plurality of cells 16i, each such cell being served by a Base Station (BS) 14i. The BSs provide radio service to all MSs within their corresponding cell. For example, in FIG. 3, BS 143 provides cellular service to MS 18 which is within the cell 163. The coexistent radio network 12, such as for example a public safety radio network, has itself a central radio station 20 providing radio coverage to its radio terminals, such as to radio terminal 22, over an area typically much bigger than a cell 16i. For example, the central radio station 20 may service a police station and thus provide radio service for police radio terminals over an entire city.
Instances arise when a public safety radio terminal such as terminal 22, served by central radio station 20, arrive in positions physically close to a BS of a cellular system, such as BS 163 of system 10. In such conditions, the radio terminal 22 receives not only a radio frequency signal 21 (attenuated because of the distant location of the terminal 22 with respect its central radio station 20) from its own central station 20, but also a strong interfering radio signal 23 from a close emitter, i.e. from BS 143, the radio frequency signal 23 being intended not for the terminal 22, but for MSs served by BS 143, like the MS 18. When the frequencies of signals 21 and 23 are too close, and when like in the example of FIG. 3 the public safety radio terminal is far from its central radio station but physically close to the interfering emitter, the downlink communications between the central station and the terminal are substantially disturbed by the so-called near-far interference, oftentimes to such an extent that the terminal 22 is no longer able to receive communication from the station 20.
Reference is now made to FIG. 4, wherein there is shown an exemplary detailed representation of the near-far interference engendered by a first system, such as a cellular system, into a second system, such as a public safety radio system. In FIG. 4, it is assumed that the cellular telecommunications system 10 shown in FIG. 3 uses the frequency spectrum X, which is divided, like in Time Division Multiple Access (TDMA) based cellular telecommunications networks in a plurality of frequency channels (all cellular systems use radio channel, but they may vary in bandwidth). For the purpose of the present example, it is assumed that the last three frequency channels at the high end of the frequency spectrum X are frequency channels A, B, and C. A Guard Band GB is allocated to separate in frequency the spectrum X used by the cellular telecommunications system 10 from another frequency spectrum Y assigned and used by the radio network 12 of a public safety organization. The frequency spectrum Y is also divided into a plurality of frequency channels, such as for example frequency channels 1, 2 and 3, and so on. FIG. 4 shows that cellular frequency channels A, B, and C are received at a given location within the cell 143 with a given power level, L1. At the same given location, because of the transmission attenuation due to the distance, the public safety radio channels 1, 2, and 3 are received with a second, much lower, power level, L2. Furthermore, as described with reference to FIGS 1.a and 1.b, the frequency channels A, B, and C engender OOBEs Axe2x80x2, Bxe2x80x2, and Cxe2x80x2. In some cases, the bandwidth assigned to the guard band GB is not sufficient for the OOBE of channels A, B, and C to fade off before xe2x80x9creachingxe2x80x9d channels 1, 2, and 3 of the other radio application. Therefore, instances arise when the power level of the OOBE of a cellular frequency channel is important enough to be comparable with the power level of some of the downlink frequency channels, such as the channels 1, 2, and 3 of the public safety radio network 12, and thus severely interfere with the public safety radio channels.
Given the life-critical nature of radio communications of the public safety organizations, the radio interference caused by cellular systems and affecting the radio channels used by the public safety organizations should be reduced.
It would be advantageous to have a method and system that solves the above-identified deficiencies. It would be of even further advantage to have a method and system that would automatically eliminate the radio interference engendered by a cellular network into a public safety organization radio network as soon as such an interference is detected.
The present invention provides such a solution.
It is therefore an object of the present invention to provide in a cellular telecommunications system, a method for reducing Out of Band radio Emissions (OOBE) of a downlink cellular channel, the method comprising the steps of:
finding an uplink radio channel currently being used by a radio terminal of a coexistent radio network for carrying out a radio communication, and determining a transmission power level of the radio communication;
determining if the uplink radio channel communication power level exceeds a predefined tolerable power level threshold;
if the uplink radio channel transmission power level exceeds the predefined tolerable power level threshold,
determining a downlink radio channel serving the same radio communication as the uplink radio channel;
determining at least one downlink cellular channel currently in use and that is likely to generate OOBE into the downlink radio channel, and further determining a level of OOBE of the at least one downlink cellular channel;
determining if a level of OOBE of the at least one downlink cellular channel exceeds a predefined tolerable OOBE threshold; and
if a level of OOBE of the at least one downlink cellular channel exceeds the predefined tolerable OOBE threshold,
reducing the level of OOBE of the at least one downlink cellular channel.
It is another object of the present invention to provide a in a cellular telecommunications system, a method for reducing Out of Band radio Emissions (OOBE) of an uplink cellular channel of a sectored cell, the method comprising the steps of:
finding an uplink radio channel currently being used by a radio terminal of a coexistent radio network for carrying out a radio communication, and determining a transmission power level of the radio communication;
determining if the uplink radio channel communication power level exceeds a predefined tolerable power level threshold;
if the uplink radio channel transmission power level exceeds the predefined tolerable power level threshold,
determining a downlink radio channel serving the same radio communication as the uplink radio channel;
determining all uplink cellular channels currently serving Mobile Stations calls in the same direction of arrival as the coexistent radio terminal;
determining a level of OOBE of each one of all uplink cellular channels currently serving Mobile Stations calls in the same direction of arrival as the coexistent radio network terminal;
determining if a level of OOBE of any uplink cellular channels exceeds a predefined OOBE threshold; and
if a level of OOBE of at least one of all uplink cellular channels exceeds a predefined OOBE threshold,
reducing the level of OOBE of the at least one of all uplink cellular channels.
It is yet another object of the invention to provide in a cellular telecommunications system, a cell radio controller comprising:
at least one radio receiver for finding a current uplink radio channel of a radio terminal of a coexistent radio network and for determining the uplink radio transmission power level;
a comparison device for determining if the uplink radio transmission power level exceeds a predefined tolerable power level threshold;
a processor for determining a downlink radio channel serving the same communication as the uplink radio channel of the radio terminal, and for further determining at least one downlink cellular channel currently in use and that is likely to generate OOBE into the downlink radio channel of the coexistent radio network, and its level of OOBE;
wherein the processor determines if the level of OOBE of the at least one downlink cellular channel exceeds a predefined tolerable OOBE threshold, and if so, instructs a radio transmitter of the cell radio controller to reduce the level of OOBE of the at least one downlink cellular channel.
It is yet another object of the invention to provide in a cellular telecommunications system, a cell radio controller comprising:
at least one radio receiver for finding a current uplink radio channel of a radio terminal of a coexistent radio network and for determining the uplink radio transmission power level;
a comparison device for determining if the uplink radio transmission power level exceeds a predefined tolerable power level threshold;
a processor for determining a downlink radio channel serving the same communication as the uplink radio channel of the radio terminal, and for further determining an identity of all uplink cellular channels currently serving a call in a direction of arrival of the coexistent system uplink transmission and their respective level of OOBEs generated into the coexistent radio network downlink channel;
wherein the processor further determines if the level of OOBEs of at least one of the uplink cellular channels exceeds a predefined tolerable OOBE threshold and if so, reduces the level of OOBE of the of at least one of the uplink cellular channels.